Electrical signal classifier utilizing magnetic elements



N av. 24,

Filed June 12, 1962 1964 R. w. GILBERT 3,158,838

ELECTRICAL SIGNAL CLASSIFIER UTILIZING MAGNETIC ELEMENTS 3 Sheets-Sheet1 FIG. a 5 5 4o I PULSE l 3g 4 SOURCE l 2 34 l I l 35 36 L J 2o '2OUTPUT \INTERROGATION SOURCE OF PULSE SOURCE ELECTRICAL INPUT SIGNAL (1)INTERROGATION PULSE SOURCE I i'l'i'l'F 4 7 CLASS n I I L4 g n -W i), 6%

|oc 24 8 2: CL ASS(n-l) I $I I r L MC g; 1 52c I 24 I 1- SOURCE OF iELECTRICAL i sl rfiglf i i i (I) i I |Ob 5g) kzne [CLASS 2 I2 I I L Wi f24 8 52b 2 2 IOo 24 2 (CLASS I O I I2 22 3, 24 28 l INVENTOR i ROSWELLw. GILBERT ATTORNEY FIG. 2

ELECTRICAL SIGNAL CLASSIFIER UTILIZING MAGNETIC ELEMENTS Filed June 12,

CLASS n INPUTS FROM CLASSIFIER CLASS CLASS 2 CLASS I "R. w. GILBERT FIG.3

3 Sheets-Sheet 2 UTILIZATION DEVICE INTERROGATION (we PULSLE SOURCE j I32 M 2 9 5 I01 28 flaw, o

52b [I| I I2 30.

so 1 SOURCE OF ELECTRICAL 5- (3 INPUT SIGNAL (1) II l CENTER CLASS 1' 1I?I II FIG. 4

INVENTOR ROSWELL W. G|LBERT 3 Sheets-Sheet 5 ATTORNEY SOURCE 0FREFERENCE CURRENT INVENTOR ROSWELL W. GILBERT R. W. GILBERT ELECTRICALSIGNAL CLASSIFIER UTILIZING MAGNETIC ELEMENTS PULSE SOURCE Nov. 24, 1964Filed June 12, 1962 32' INTERROGATION FIG. 5

SIGNAL CURRENT SOURCE OF ELECTRICAL United States Patent 3,158,838ELECTRICAL SIGNAL CLASSIFIER UTILIZING MAGNETIC ELEMENTS Roswell W.Gilbert, East Orange, N.J., assignor to Weston Instruments, Inc., acorporation of Texas Filed June 12, 1962, Ser. No. 201,998 Claims. (Cl.340-472) This invention relates to apparatus for determining theamplitude of an electrical signal and, more particularly, to apparatusemploying magnetic elements for classifying an electrical signalaccording to its amplitude.

In the field of industrial control it is often necessary to determinewhether the amplitude of an electrical signal, which may be a functionof temperature, thickness, pressure, etc., is within acceptableamplitude limits, is less than such limits, or is greater than suchlimits. For example, a conventional thickness gauge may provide acontinuous electrical output signal representative of the thickness of asheet of steel. It may be desirable in a rolling mill operation, forexample, to maintain the sheet thickness within certain tolerancelimits; i.e., within a class or range of acceptable thicknesses. Anythicknesses above or below this range of desired'thicknesses areunacceptable. Depending upon whether the thickness of the steel sheet isabove or below the acceptable range of thicknesses, conventional controlcircuitry may be energized to either increase or decrease the pressureof the rollers that are forming the sheet of steel. Alternatively, onemay wish to continuously measure the thickness of a roll of steel sheetand classify the portions of the roll (which typically vary inthickness) according to their thickness.

Existing apparatus used to classify an electrical signal into classes,each typically encompassing varying ranges of amplitude, have beensomewhat complex and hence relatively costly. For example, some systemshave used full analog-to-digital conversion techniques and then digitalcomputer techniques for classifying the digital representation of theelectrical signal. Such systems are adequate, but unfortunately arequite costly. I

It is therefore an object of this invention to obviate the disadvantagesof the prior art electrical signal classifiers.

Another object of this invention is to facilitate the classification ofan electrical signal into amplitude ranges by relatively simple yetprecise apparatus.

Still another object of this invention is to use magnetic comparators toclassify an electrical signal into amplitude I ranges.

In an illustrative embodiment of this invention, the apparatus forclassifying an electrical input signal according to its amplitudeincludes a plurality of pulse type magnetic comparators. input winding,an interrogation winding, a- 7 reference winding, and an output windingon a single saturable magneticcore. A plurality of sources of referencecurrent, each source connected to the reference winding of a differentone of the magnetic comparators for magnetizing the magnetic core ofeach amplifier in a first sense. The signal windings are connected inseries circuit and the input electrical signal is applied to the seriescircuit in such polarity as tomagnetize the core of each comparator in asecond sense opposite the first sense. The interrogation windings of thecomparators are connected in series and an interrogation pulse ofsuitable polarity is applied across the series combination to magnetizethe core of each comparator in the first sense which aids the referencecurrent. The interrogation pulse passes through to the output winding ofthat one comparator corresponding to the amplitude class into which theamplitude of the input electrical signal falls. The comparator passingthe interrogation pulse is the one whose reference current amplitude isless than but closest to the amplitude of the input signal.

Further advantages and features of this invention will become apparentupon consideration of the following description read in conjunction withthe drawings wherein:

FIGURE 1 is a part schematic and part block diagram of a magneticcomparator suitable for use with this invention;

FIG. 2 isa part schematic and part block diagram of an electrical signalclassifying apparatus constructed in accordance with one embodiment ofthis invention;

FIG. 3 is a block diagram of a logic circuit that may be used toeliminate ambiguities in the output of the signal classifier of FIG. 2,in the event the amplitude of the input Each of the magnetic comparatorshas an electrical signal falls on or close to a class amplitudeboundary;

FIG. 4 is a part block and part schematic diagram of an electricalsignal classifier constructed in accordance with another embodiment ofthis invention; and

FIG. 5 is a part block and part schematic diagram of an electricalsignal classifier constructed in accordance with a third embodiment ofthis invention.

Referring to FIG. 1, there is illustrated a pulse type magnetic compaator or switching circuit depicted by the dotted rectangle 10 that maybe used with the electrical signal classifier of this invention. Theterms magnetic comparator or magnetic switching circuit are usedsynonomously herein to mean a device using wound saturable magneticcores, either alone or in combination with other circuit elements, tosecure control, or amplification if desired, and which are based on aprocess of magnetizing a core or cores by a pulsating magnetomotiveforce and by simultaneously applied unidirectional magnetometive forces.,Itmay be noted that the magnetic comparator illustrated in FIG. 1 ismerely an illustration of a typical magnetic amplifier that may be usedwith this invention; as any other suitable magnetic amplifier may beused. The magnetic comparator 10 includes a saturable magnetic core 12which may be toroidal in form, has a low coercivity to permit its easymagnetic saturation, and may be tape wound or laminated. A suitablematerial available commercially for the core 12 is supermalloy. The core12 has four windings each wound in the same direction on the core andeach having the same number of turns. These windings include a signalinput winding 14, a reference winding 16, an interrogation winding 18,and an output winding 20. The ends of each of the windings 14, 16, 18,and 29 are connected respectively to first and second input terminals22, 24, 26, and 28 which in turn are connected to appropriate input andoutput circuitry for the comparator it). Thus a source of an electricalinput signal 30, which is to be classified according to its amplitude,is connected to the input terminals 22 such as to drive or magnetize thecore 12 in a first sensetoward a state, which for convenience,n1ay betermed the P sense of magnetic saturation. 1

In like manner the reference winding input terminals 24 are connected toa reference current sourcetwhich may include a source of potential,illustrated by the battery 50, connected in series with a variableresistor 52. The current supplied by the: reference current source is orsuch polarity as to establish a magnetic. flux in the core 12. in asecond sense opposite to the first sense. This second sense will bereferred to I as the N sense of magnetization. The interrogation windingterminals 26 pulse source 32 which provides a negative-goinglwithrespect to ground) interrogation pulse 34. Since the windings are allwound in the same direction, the interrogation pulse 34 drives the core12 toward the N sense of magnetization, i.e., in the same sense as thereference current. I

The negative-going interrogation pulse 34 1 preferably has a sharp risetime 35 and a slower fall and recovery are connected across aninterrogation amasse period 36. The slower fall and recovery period 36prevents ringing in the magnetic circuitry. The pulse is D.-C. restoredby a conventional D.-C. restorer 38 (which includes a parallel connecteddiode and resistor in series with a capacitor) to maintain the base line37. The interrogation pulse 34 may be derived initially from anysuitable pulse source 40 such as a blocking oscillator. Lastly, theoutput winding terminals 28 are connected between ground and a suitableoutput pulse line which may be connected to suitable utilizationcircuitry which will be described in conjunction with FIGS. 2 and 3.

The operation of the magnetic comparator It is conventional. Dependingupon the adjustment of the variable resistor 52, the battery 59 passes areference current I of varying magnitude through the reference currentwinding 16. It has been stated that for a reference current of thepolarity indicated, a magnetic fiux is established which drives the core12 in the N sense of magnetization. The input electrical signal I, whichis to be classified establishes a magnetic flux in the core 12 oppositeto that of the reference current, i.e., such as to drive the core 12toward the P sense of magnetization. Depending upon the relativemagnitudes of the reference current 1,, and the input signal current I,the net magnetization of the core 12 is in the P or N sense ofmagnetization. In the event the signal current I and the referencecurrent I are equal in amplitude, the core 12 remains substantiallyimmagne-tized.

Now with the application of the interrogation pulse 34, its resultingmagnetizing, or magnetomotive force, drives the core 12 in the N senseof magnetization, which is in the same sense as the magnetizing forceprovided by the reference current I If the amplitude of the signalcurrent I is smaller than the amplitude of the reference current I thenet magnetization (I -I) of the core 12 also is in the N sense. Using acore 12 having a low coercivity, the net magnetizing force (I -J)typically is sutficient to magnetically saturate the core 12. Hence,little or no flux change occurs within the core 12 with the advent ofthe interrogation pulse 34 and no output signal is induced in the outputwinding 20. On the other hand, if the signal current I is larger thanthe reference current l the net magnetization of the core 12 is in the Psense. The interrogation pulse 34, producing a magnetizing force in theopposite, or N sense, causes a flux change in the core 12 which couplesthe interrogation pulse into output winding 20.

The interrogation pulse source 32 should be capable of delivering acurrent of suificient magnitude to overcome the maximum netmagnetization (1-19) of the core 12 due to the maximum anticipatedamplitude of the signal current I. Otherwise the interrogation pulsewill be insuflicient in amplitude to flux link the core, and no outputsignal will develop. Additionally, the interrogation pulse 34 shouldhave a voltage-time integral at least somewhat smaller than the fluxlinkages established in the core 12 by the net magnetizing current (l l'The total number of flux linkages produced in the core 12 by theinterrogation pulse is expressed by Faradays Law. 'Fa'radays Law equatesthe voltage-area of the exciting current, expressed in volt-seconds, toflux linkages (number of turns in the Winding multiplied by the fluxlines linking them). If the interrogation pulse has a volt-second areathat is too large, the core 12 becomes magnetically saturated and theinterrogation pulse 34 produces unwanted pulses in other magneticamplifiers as will be described in conjunction with FIG. 2. Thesecriteria allow most of the voltage drop in the interrogation circuit tooccur across only one magnetic amplifier and yet avoid magneticallysaturating the core 12 of that one amplifier.

In FIG. 2 there is illustrated an electrical signal classifier capableof classifying an electrical input signal I into one of four differentclasses according to its amplitude; namely, Class 1, Class 2, Class (n1)and Class n.

Separate magnetic comparators 19a, 10b, 10c, and 10d, of the type shownin FIG. 1, are provided for each of the classes 1, 2, n-1, and n. Theinterrogation input terminals 26 of each of the comparators 10a, ltib,10c, and ll-tld, are serially connected across the interrogation pulsesource 32. In like manner, the signal input terminals 22 of each of thecomparators 10a, 10b, 10c, and 10d, are serially connected across theelectrical input signal source 30 in the same polarity. Individualoutput lines are connected across the output terminals 28 of each of thecomparators 10a, 10b, 10c, and 10d. Suitable reference current sourcesare connected to the reference current input terminals 24 of each of theClass 2, Class (n1), and Class 11 comparators 10b, 10c, and 10d,respectively. The reference currents, which may be designated I I and Ifor the respective Class 2, Class (n1) and Class n comparators,establish the limits or boundaries to the current amplitude rangesdefining the several classes into which the electrical signal from thesource 30 is to be classified. These reference currents may be derived,as in FIG. 1, from a source of potential illustrated as the battery St),the positive terminal of which is connected through parallel variableresistors 52b, 52c, and 5211 to the lower one (in the drawing) of thereference current input terminals 24 of the respective comparators 10b,19c, and 10d. The particular amplitudes of the reference currents areadjustable by varying the resistors 52b, 52c, and 52d. It may be notedthat the Class 1 comparator 10a has no reference current and hence, aswill be described hereinafter, provides an output pulse in the event theinput signal I has an amplitude more than zero and less than thereference current I The reference currents are selected such that I I IHence the Class 2 comparator covers the amplitude range I I I the Classn--l comparator, the range I l I and the Class n'comparator the range 11 In the operation of the signal classifier of FIG. 2, let us assumethat the input signal I is greater in amplitude than the referencecurrent I but less in amplitude than the reference current I Under theseconditions the Class n1 and class It comparators 19c and 10d,respectively, are magnetically saturated, i.e., their cores 12 (FIG. 1)are magnetically saturated in the N sense of magnetization since thereference currents I and I are greater in amplitude than the signalcurrent I. The Class 2 magnetic comparator ltib, on the other hand, ismagnetized in the first, or P sense of magnetization since I 1 In likemanner the Class 1 comparator 10a is magnetized in the P sense by theinput signal current I. Now with the occurrence of the negative-goinginterrogation pulse 34 (FIG. 1) from the interrogation pulse source 32,a magnetizing force in the second or N sense is applied to the cores 12(FIG. 1) of each of the amplifiers 19. Since the class (rt-1) and class11 comparator I00 and 10d, respectively, are already magnetized in the Nsense, little or no change in magnetic flux occurs and hence no outputpulse results at either of their output terminals 28.

Such is not the case in the Class 2 magnetic comparator 10b. Theinterrogation pulse 34 (FIG. 1) drives its core 12. (FIG. 1) in the Nsense of magnetization. Since its core 12 was magnetized in the P senseby the input signal I, the resulting flux change induces an output pulseacross its. output terminals 28. This output signal correctly denotesthe input signal I which has an amplitude greater than I but less than IThe Class 1 comparator 16a causes little or no output pulse even thoughit also is magnetized in the same sense as the class 2 comparator 1%.Its core 12 (FIG. 1) is more heavily magnetized in the P sense by theinput signal current I than the core 12 of the class 2 comparator. Hencethe flux build-up in the class 2 comparator Jlhb occurs more quicklywith the occurrence of the interrogation pulse. With the quicker fluxbuild-up in the class 2 comparator 10b, its interrogation windingpresents a relatively high impedance to the interrogation pulse currentto the extent that no other cores are flux linked to any appreciableextent.

The function of the interrogation pulse 34 (FIG. 1) is to flux link thecore of that comparator having the least net magnetization of oppositesense to the sense of the magnetizing force provided by theinterrogation pulse. This in effect transfers the pulse to thecorresponding output terminals 28 of that comparator 10 whose core hasthe least net magnetization of opposite sense to the sense of theinterrogation pulse.

If at the instant of interrogation the amplitude of the input current Iequals or is extremely close to the amplitude of one of the referencecurrents, a boundary condition exists and two partial pulses from eachof two comparators 10 may occur instead of asingle pulse from a singleelement. For example, if I=I the core 12 (FIG. 1) of the class (n-1)comparator 100 is llux linked .by the input signal current 1. Underthese conditions the voltage-time integral of the interrogation pulse 34may be sufficiently great to magnetically saturate the core of the class(n-l) comparator 100 in the N sense of magnetization. Upon saturation,the impedance presented to the interrogation current drops tosubstantially zero. The interrogation pulse voltage is then applied tothe class 2 magnetic comparator 101) such that a partial pulse may bedelivered on the output winding of the class 2 comparator in addition tothe class (n1) comparator 10c. This is a boundary ambiguity and may beavoided by the utilization of the logic circuit illustrated in FIG. 3.

In FIG. 3 the set inputs (S) of each of four flip-flops 100, 102, 104,and 106 are connected to the respective output terminals 28 of the class1, class 2, class (n1) and class :1 amplifiers 10 (FIG. 2). Each of theflip-flops 100, 102, 104, 106 have aset input (S), a reset input (R),and corresponding 1 and 0 outputs. The application of a high levelsignal or pulse to the set input terminal S of any flip-flop provides acorresponding high signal level on its 1 output terminal. Acorresponding high signal level or pulse on the reset input terminal (R)provides a high signal output level on the 0 output terminal.

The 1" outputs of each of the flip-flops 100, 102, 104,

and 106 are connected respectively to a suitable utilization device 140which may receive the pulse information.

Additionally the 1 output of the first flip-flop 100 is connected in theforward conducting direct-ion through respective diodes 108, 110, and112 to the reset inputzs R of the second flip-flop 102, the thirdflip-flop 104, and the fourth fiip-fiop 106. In like manner the 1 outputof the second flip-flop 102 is connected through the respective diodes114, 116, and 118 in their forward conducting direction tothe respectivereset inputs R of the first, third and fourth flip-flops, 100, 104, and106. Also the 1 output of the third flip-flop 104 is connected throughrespective diodes120, 122;, and 124 to the reset inputs R of the first,second, and fourth flip-flops 100,102, and 106, respectively. Finallythe 1 output of the fourth flip-flop 106 is connected through respectivediodes 12 6, 128, and 130 in their forward conduction direction to thereset inputs R of the first, second, and third flip-flops 100, 102, and104, respectively. A set input pulse, available at the terminal 131 maybe connected through respectivediodes132, 1'34, 136, and 138, in theirforward conducting direction, to the reset input R of each of the first,second, third, and fourth flip-flops 100, 102, 104, 106, respectively.

The application of a positive going pulse at the set input terminal 130resets each of the flip-flops 100, 102, 104, 106 such that their 1outputs are at a low signal level. It may be observed that thesefiip-flops are interconnected logically by the several diodes so thatonly one flip-flop may remain in the 1" state. Assume, for example, thatthe class (rt-1) comparator 100 (FIG. 2)

output terminals 28, the second flip-flop 102 is immediately setproviding a high level 1 output signal. The high level 1 output passesthrough the several diodes, 114, 116, and 118 to maintain each of theremaining flipi'lops 100, 104, 106 reset. Thus when the pulse from theclass 2 amplifier output terminals 28 is applied to the set input S ofthe third flip-flop 104, it is disabled and remains reset. Only thesecond fiip-flop 102 provides a high level output signal. Hence theambiguity is resolved.

In FIG. 4 there is illustrated still another embodiment of an electricalsignal classifier constructed in accordance with this invention. Theclassifier illustrated in FIG. 4 is substantially identical to thatillustrated in FIG. 2, the difference being that the classifier of FIG.4 is useful for classifying electrical input signals representing plusand minus deviations from a zero or centerpoint which correspondspossibly to a bogey dimension of a sheet of steel, for example. In FIG.4 there are illustrated five magnetic comparators 10c, 10 10g, 10h, andNi or" the type illustrated in FIG. 1. Each of the magnetic comparators10 have their interrogation terminals 26 connected in series across theinterrogation pulse source 32 and their output terminals 28 connected toindividual output lines in substantially the same manner as in FIG. 2.The third magnetic comparator 10g has no input reference currentconnection to its terminals 24 and hence corresponds to a centerclassification in which the input current varies positively andnegatively with respect to zero current. The first and secondcomparators 10s and 10], respectively, have their reference windinginput terminals 24 connected, respectively, to receive referencecurrents I and I in which l I through the respective variable resistors52a and 52.5 from the negative side of a source of potential illustratedas the battery 50. The fourth magnetic comparator 10h has its referencewinding terminals 24 serially connected to the reference winding inputterminals 24 of the second comparator 10 but with the connectionsreversed such that its reference current is -1 instead of +1 In likemanner the reference winding input terminals 24 of the fifth comparator101' are serially connected with the input terminals 24 of the firstcomparator 10c but again with the connecting wires interchanged suchthat its reference current is I;, instead of +1 With these severalreference currents establishing the class boundaries, the firstcomparator 10c corresponds to the input signal I l In like manner thesecond comparator covers the class I l I The third comparator 10gcorresponds to the class -I I I the fourth comparator 10h corresponds tothe class I I -I and the fifth comparator 10i covers the class where theinput current is I -.I The source of the electrical input signal 30 isconnected across the series combination of each of the input signalwinding terminals 22. The center class comparator 10g is provided with arectifier network 148 to pass the input signal current it regardless ofpolarity in the same direction through its signal input Winding 14 (FIG.1). The bypass functions to pass the signal current in the properdirection to magnetize the core 12 (FIG. 1) of the center classcomparator 10g in a sense opposite that of the interrogation Winding 18(FIG. 1). Additionally, the connections of the input signal source 30 tothe input signal terminals 22 of the fourth and fifth comparators 10hand 101' are reversed to accommodate negative input currents.

The rectifier network 143 includes first and second diodes 150 and 152which are serially connected to the.

respective terminals 22 of the third comparator 10g and connected withrespect to polarity to pass a positive going current from the'inputsignal source 30. In like manner a third diode 154 has its anodeconnected to anode of the second diode 152 and its cathode connected tothe anode of the first diode lt The fourth diode 156 has its anodeconnected to the cathode of the second diode 152 and its cathodeconnected to the cathode of the first diode 150. Thus connected, thethird and fourth diodes 15d and 156 pass a negative input signal (withrespect to ground) through the input signal winding 14 (FIG. 1) in thesame direction as a positive input signal.

Depending upon the polarity and amplitude of the input signal I from thesource 36, one of the five comparators lite through ldi, inclusive,passes the interrogation pulse to a suitable utilization device. Theoperation of the classifier is substantially the same as thatillustrated in FIG. 2 and need not again be described. Since theconnections of the input signal to the fourth and fifth comparator 1011and its input winding terminals 22 is reversed, negative input signalsbehave as the positive signals as described in FIG. 2. Negative inputsignals applied to the first two comparators lite and lit) and positiveinput signals applied to the fourth and fifth comparators itih andfttii, drive their cores in the N sense of magnetization as do thereference and interrogation currents. Hence no output signals occur intheir output windings.

FIG. 5 illustrates still another embodiment of the present inventionwhich is an alternative to that illustrated in FIG. 4. The embodiment ofIG. 5 simplifies that of FIG. 4 by introducing the input signal currentdirectly into the interrogation pulse windings, thereby eliminating theneed for the signal windings of each of the magnetic comparators. Theembodiment of FIG. 5 classifies an input signal according to itsamplitude and polarity into one of seven classes depending upon whetherthe input signal ii is less than or more than the class boundariesdetermined by the several reference currents i1 :12, 01' il In HG. 5there are illustrated seven magnetic comparators l1ailg inclusive. Themagnetic comparators 11 are of substantially the same type illustratedin PEG. 1, except that they have no signal input winding 14 (FIG. 1).Thus each of the output windings 20 (FIG. 5) is connected to a suitableutilization device 17%. A source of reference current ltiti providespositive reference currents (with respect to ground) of l I I Thesereference currents are connected to selected ones of the comparators 11ato 11g to establish the several class boundaries. The first referencecurrent I is serially connected to the reference current windings 16 ofthe fourth and fifth comparators 11a and 11s with the connections to thefourth comparator 11d reference winding 16 reversed to drive the core 12in the N sense of magnetization rather than the P sense.

In like manner the I reference current is serially connected through thereference windings 16 of the third and sixth comparators lilo and lit)With the connection to the third comparator llc reference winding 16reversed to drive its core 12 in the N sense of magnetization. Lastly,the reference current I from the source we is serially connected throughthe reference current windings 16 of the first, second, and seventhcomparators Ila, 11b, and 11g, respectively. The connections to thefirst and second comparator llla and 12th reference windings 16 isreversed to drive their respective cores 12 in the N sense ofmagnetization. These referennce currents establish the several classes:

The interrogation pulse source 32, which may be substantially the sameas the source 32 (FIG. 1), is connected to pass positive-going (withrespect to ground) current pulses through the interrogation windings 18of each of the comparators Ila to llg, inclusive. The positive-goinginterrogation pulses drive the core 12 of each comparator in the P senseof magnetization and otherwise have the same wave form (with theirpolarity inverted) as the pulses 34 (FIG. 1).

Thus far described, the signal classifier of FIG. 5 is substantially thesame as those previously described herein. In accordance with thisembodiment of the invention, however, the source of electrical signalcurrent 30 is connected, through the cathode side of a diode 166 and aserially connected choke 162, across the series connected, interrogationwindings 18 of the comparators 11a to 'llg. This provides the currentpath through the interrogation windings 13, when the input signal isnegative going with respect to ground. An alternative current. path isprovided for positive-going input signals through the anode side of asecond diode res and a choke 164 to the junction 177. between thewindings 18 of the first and second comparators 11a and 11b.Positive-going signals thus are connected across the interrogationwindings 18 of each of the second through seventh comparators 11bthrough llg, inclusive.

The operation of the embodiment of FIG. 5 is quite similar to that ofFIG. 4. The interrogation pulse from the source 32. flux links that onecomparator Ila-11g Whose core 12 is nearest zero magnetization in the Nsense, and passes a pulse to the output winding 24) of that comparator.The interrogation pulse passes through all other comparators whose coresare more heavily magnetized in the negative sense N or magnetized in thepositive sense P.

Assume, for example, that the input signal I is greater in negativeamplitude than the reference current I In this instance the core 12 ofthe seventh comparator Hg is magnetically biased slightly in the N senseof magnetization. With the occurrence of the interrogation pulse, whichdrives each of the cores 12 toward the P sense of magnetization, anoutput pulse is induced in the output winding Ztt of the seventhcomparator Hg. The cores 12 of the fifth and sixth comparators title and10f are also magnetically biased in the N sense of magnetization, butprovide no output pulse in that the primary voltage drop occurs acrossthe interrogation winding 18 of the seventh comparator llg since itscore is the most easily driven in the P sense of magnetization. In likemanner, each of the first four comparators Ila to 11d, inclusive, ismagnetically saturated in the N sense of magnetization by both thereference current and the signal current. The magnetizing forcesproduced by the reference and signal currents are too great to permitthe interrogation pulse to have any effect for the same reason as wasdescribed in connection with the sixth comparator 11]". Hence, only oneoutput pulse is provided, and that on the output line of the seventhcomparator 11g to properly denote that the input signal current isgreater in negative magnitude than the reference current -I As anotherillustrative example, assume that the amplitude of the input signalcurrent I falls between I and I In this instance, since the referencecurrent of the second comparator 11b exceeds the amplitude of the signalcurrent I, its core 12 is magnetically biased slightly in the N sense.Hence the interrogation pulse, applying a magnetizing force in the Psense, switches the core 12 of the second comparator 10b to the P senseof magnetization. This flux linkage produces a magnetic flux changewhich results in an induced output pulse in the output winding 20, ofonly the second comparator. Since most of the voltage drop occurs acrossthe interrogation winding 13 of the second comparator lllb, there isinsufficient current to produce any output pulse in the first comparatorltila. It may be recalled that the first comparator 11a receives nosignal current due to the by-pass connection of the second diode 208 andhence is very heavily driven in the N sense of magnetization.

Each of the remaining comparators 11c through 11g, inclusive, providesno output pulse since the core 12 of each is already magnetized, and infact are magnetically saturated in due to their low coercivity, in the Psense. In the third comparator 110, for example, the signal currentamplitude I exceeds that of the reference current. The signal current Iis of such porality as to drive that core 12 in the P sense ofmagnetization. In the last three comparators lle thorugh 11g, inclusive,both the reference and signal currents drive the respective cores 12 inthe P sense of magnetization.

If, for example, the input signal I amplitude is greater than theamplitude of the positive reference current I the core 12 of the secondcomparator 11b has a net magnetization in the P sense, preventing anyoutput pulse. This leaves only the first comparator 11a core 12 that ismagnetized in the N sense by the reference current I and hence the fluxchange occurs therein to induce an output voltage on the output winding20 of the first comparator 11a.

It is to be understood that the number of turns of the several signaland reference windings in the several comparators used in the severalembodiments of this invention, may be varied and be proportioned toobtain various proportional responses. Additionally, the windingdirection may be designed to accommodate either positive or negativesignal currents. The classifier of this invention has a particularadvantage in that the isolated input windings permit differential modeinput circuits to be used. i

There has thus been described, an improved electrical signal classifierthat is simple, accurate, and relatively inexpensive. The boundarylevels between classes are easily and relatively precisely establishedand may be quickly changed merely by changing the amplitude of areference current as described.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

I claim:

1. Apparatus for classifying an input electrical signal according to itsamplitude into one of a plurality of amplitude defining classescomprising, in combination,

a plurality of saturable magnetic comparators each having first, second,and third input windings and an output winding,

a source of interrogation pulses,

means connecting said first input windings in series across said sourcefor generating an output signal in said output windings,

a plurality of reference current sources each providing a differentamplitude of reference current,

means connecting each of said reference current sources to a differentone of the second input windings in such polarity as to reduce theamplitude of said output signal, and

means applying said input signal to the third input winding of each ofsaid comparators in such polarity as to increase the amplitude of saidoutput signal, whereby said output signal exists substantially only onthe output winding of that one comparator whose reference currentamplitude is less than the amplitude of said input signal by the leastamount, thereby to provide an indication of the amplitude class of saidinput signal.

2. The apparatus set forth in claim 1 wherein each of said interrogationpulses each has a potential-time integral less than that required tomagnetically saturate said one magnetic comparator, and a peak amplitudegreater than the difference between said input signal and any of saidreference currents.

3. Apparatus for classifying an input electrical signal according to itsamplitude into one of a plurality of amplitude defining classescomprising, in combination,

first, second, and third magnetic switching circuits each having aseparate output winding,

a source of interrogation pulses,

means serially connecting a first winding of each of said switchingcircuits across said source of inter rogation pulses for generating anoutput signal in said output windings,

a source of reference current,

means serially connecting the second input windings of the first andthird ones of said switching circuits across said source of referencecurrent to reduce the amplitude of said output signal from said firstand third switching circuits,

means applying said input signal across a serially connected third inputwinding of each of said switching circuits, said input signal beingapplied inone polarity to the third input winding of said firstswitching circuit to increase the amplitude of said output signal, andin another polarity opposite said first polarity to the third inputwinding of said third switching circuit, thereby to provide an outputsignal on the output winding of that one switching circuit whosereference current is of the same polarity as and has an amplitude lessthan the amplitude of said input signal by the least amount, thereby toclassify said input signal of either polarity into a class in accordancewith the amplitude and polarity of the reference currents.

4. The apparatus set forth in claim 3 wherein,

the third input winding of saidsecond input circuit includes a diodenetwork means for passing said input signal therethrough in the samedirection regardless of polarity.

5. The apparatus set forth in claim 4 wherein said interrogation pulsehas an energy content less than that required to magnetically saturateany one of said magetic switching circuits.

6. Apparatus for classifying an input electrical signal according to itsamplitude into one of a plurality of amplitude defining classescomprising, in combination,

first, second, and third magnetic switching circuits each having aseparate output winding,

a source of interrogation pulses,

means serially connecting the first windings of each of said switchingcircuits across said source of interrogation pulses for generating anoutput signal in said output windings,

a source of reference current,

means serially connecting the second input windings of the first andthird ones of said switching circuits across said source of referencecurrent to reduce towards zero said output signal from said firstswitching circuit,

means for applying said input signal of one polarity circuit, meansapplying said input signal of a polarity opposite said one polarityacross the serially connected third input windings of each of saidsecond and third switching circuits; thereby to provide an output signalon the output winding of that one switching circuit whose referencecurrent amplitude is less than the amplitude of said input signal of thesame polarity by the least amount, thereby to classify said input signalof either polarity into a class in accordance with the amplitude andpolarity of said reference current sources. 7. Apparatus for classifyingan input electrical signal according to its amplitude into one of aplurality of am- 75 plitude defining classes comprising, in combination,

across the third input winding of said first switching 1. l a pluralityof pulse type magnetic comparators each having an input winding, aninterrogation winding, a reference winding and an output winding mountedon a single saturable magnetic core, a plurality of sources of referencecurrent, means connecting each of said sources of reference current tothe reference winding of a different one of said comparators forapplying a magnetomotive force to each of said cores in a first sense,

means connecting each of said input windings in series,

means for applying said input signal across said series connected inputwindings for applying a magnetomotive force to each of said cores in asecond sense opposite said first sense,

a source of interrogation pulses,

means connecting each of said interrogation windings in series acrosssaid source of interrogation pulses for applying a magnetomotive forceto each of said cores in said first sense with the occurrence of eachpulse, thereby to provide an output signal in the output winding of thatone comparator whose reference currentarnplitude is less than theamplitude of said input signal by the least amount, thereby to classifysaid input signal into said amplitude classes in accordance with theamplitudes of said reference current sources.

8. The apparatus set forth in claim 7 wherein said interrogation pulseseach have a voltage-time integral less than the flux linkage integral inany of said cores over the time duration of said interrogation pulses.

9. The apparatus set forth in claim 8 wherein said interrogation pulseseach have a peak current amplitude sutficient to overcome the maximumnet magnetization of any of said cores due to the maximum anticipatedamplitude of the input signal.

10. Apparatus for classifying an input electrical signal according toits amplitude into one of a plurality of amplitude defining classescomprising, in combination,

a first, second, and third set of pulse type magnetic comparators eachhaving an input winding, an interrogation winding, a reference winding,and an output winding mounted on a single saturable magnetic core,

a plurality of sources of reference current,

means serially connecting each of said sources of reference current tothe reference winding of a different one of said first and thirdcomparators for applying a magnetomotive force in each of said cores ina first sense,

means connecting the input windings of said first and second comparatorsin series-subtractive relationship to the input Winding of said thirdcomparator,

means for applying said input signal across said series connected inputwindings for applying a magnetomotive force to each of said cores in asecond sense opposite said first sense, v

by-pass means connected across the input winding of said secondcomparator for permitting currents of either polarity to flow throughits input Winding in the same direction,

a source of interrogation pulses,

means connecting each of said interrogation windings in series acrosssaid source of interrogation pulses for applying a magnetomotive forceto each of said cores in said first sense with the occurrence of eachpulse, thereby to provide an output signal in the output Winding of thatone comparator whose reference current amplitude is less than theamplitude of said input signal by the least amount, thereby to classifysaid input signal into said amplitude classes in accordance with theseveral current amplitudes of said reference current sources.

References Cited in the file of this patent UNITED STATES PATENTS2,486,390 Cunningham Nov. 1, 1949 2,541,039 Cole Feb. 13, 1951 2,945,963Marschall July 19, 1960 2,962,704 Buser Nov. 29, 1960 3,050,713 HarmonAug. 21, 1962

1. APPARATUS FOR CLASSIFYING AN INPUT ELECTRICAL SIGNAL ACCORDING TO ITSAMPLITUDE INTO ONE OF A PLURALITY OF AMPLITUDE DEFINING CLASSESCOMPRISING, IN COMBINATION, A PLURALITY OF SATURABLE MAGNETICCOMPARATORS EACH HAVING FIRST, SECOND, AND THIRD INPUT WINDINGS AND ANOUTPUT WINDING, A SOURCE OF INTERROGATION PULSES, MEANS CONNECTING SAIDFIRST INPUT WINDINGS IN SERIES ACROSS SAID SOURCE FOR GENERATING ANOUTPUT SIGNAL IN SAID OUTPUT WINDINGS, A PLURALITY OF REFERENCE CURRENTSOURCES EACH PROVIDING A DIFFERENT AMPLITUDE OF REFERENCE CURRENT, MEANSCONNECTING EACH OF SAID REFERENCE CURRENT SOURCES TO A DIFFERENT ONE OFTHE SECOND INPUT WINDINGS IN SUCH POLARITY AS TO REDUCE THE AMPLITUDE OFSAID OUTPUT SIGNAL, AND MEANS APPLYING SAID INPUT SIGNAL TO THE THIRDINPUT WINDING OF EACH OF SAID COMPARATORS IN SUCH POLARITY AS TOINCREASE THE AMPLITUDE OF SAID OUTPUT SIGNAL, WHEREBY SAID OUTPUT SIGNALEXISTS SUBSTANTIALLY ONLY ON THE OUTPUT WINDING OF THAT ONE COMPARATORWHOSE REFERENCE CURRENT AMPLITUDE IS LESS THAN THE AMPLITUDE OF SAIDINPUT SIGNAL BY THE LEAST AMOUNT, THEREBY TO PROVIDE AN INDICATION OFTHE AMPLITUDE CLASS OF SAID INPUT SIGNAL.